Dissolution of lanthanum fluoride precipitates



Nov. 10,. 1959 B. A. FRIES DISSOLUTION 0F LANTHANUM FLUORIDE PRECIPITATES Filed March 7. 1946 2 Sheets-Sheet 2 for 09/7 frv'fuge 50 w/ Wash Jez Wash 75 Waste Za 0H Prcz'o/ta/on 4 N KOH Carry Out //7 Prec/p/zazor W/zh La/OH); Ay/Zat/on Then Pr'ec/p/zai/on f Supernatant Cenzr/fuge E Waste 2 N K OH a(0H) Washes 75 Waste Carry Out /n Prec/p/zaior Wit/1 Wash Lam/19 H20 Ag/zai/on Then Carrying Pu 75 Waste Cen zr/fuge 75 Waste Wa heaLa 0h Cak (g'an a/'/ 7//7 g Puf IN VEN TOR. Bernard A fives F'IE. B

BY WIL-M Unite tes DISSOLUTION F LANTHANUM FLUORIDE PRECIPITATES Application March 7, 1946, Serial No. 652,829

2 Claims. (Cl. 23-145) This invention relates to a procedure for processing materials containing the element of atomic number 94, known as plutonium, for separating the plutonium from extraneous matter such as substances of the kind present in neutron irradiated uranium as exemplified by uranium and especially fission products, and the like radioactive contaminants. More particularly, this invention concerns a separatory and concentration procedure involving the use of a fluoride type of carrier wherein certain improved procedure is employed in treating the carrier.

As described herein, the isotope of element 94 having a mass of 239 is referred to as 94 and is also called plutonium, symbol Pu. In addition, the isotope of element 93 having a mass of 239 is referred to as 93 Reference herein to any of the elements or to the term plutonium values is to be understood as denoting the element generically, Whether in its free state or in the form of a compound, unless indicated otherwise by the context.

Elements 93 and 94 may be obtained from uranium by various processes which do not form a part of the present invention including irradiation of uranium with neutrons from any suitable neutron source, but preferably the neutrons used are obtained from a chain reaction of neutrons with uranium.

Naturally occurring uranium contains a major portion of U a minor portion of U and small amounts of other substances such as UX and UX When a mass of such uranium is subjected to neutron irradiation, particularly with neutrons of resonance or thermal energies, U by capture of a neutron becomes U which has a half life of about 23 minutes and by beta decay becomes 93 The 93 has a half life of about 2.3 days and by beta decay becomes 94 Thus, neutron irradiated uranium contains both 93 and 94 but by storing such irradiated uranium for a suitable period of time, the 93 is converted almost entirely to 94 In addition to the above-mentioned reaction, the reaction of neutrons with fissionable nuclei such as the nucleus of U results in the production of a large number of radioactive fission products. As it is undesirable to produce a large concentration of these fission products which must, in view of their high radioactivity, be separated from the 94 and further as the weight of radioactive fission products present in neutron irradiated uranium is proportional to the amounts of 93 and 94 formed therein, it is preferable to discontinue the irradiation of the uranium by neutrons when the combined amount of 93 and 94 is equal to approximately 0.02 percent by weight of the uranium mass. At this concentration of these substances, the concentration of fission elements which must be removed is approximately the same percentage.

A number of processes have already been proposed for accomplishing the separation and concentration of Pu. Certain of these processes are generically known as the bismuth phosphate type process and the wet fiuo ride type of process. These processes are the invention of others and the details of the processes are described in copending applications as for example application Ser. No. 519,714, now US. Patent No. 2,785,951, issued March 19, 1957, to be referred to hereinafter, which gives details relative to the aforementioned processes. Consequently, all of the details of operation of the aforementioned processes are not described herein.

In one type of procedure in successful use it is customary to utilize both the bismuth phosphate treatment and the lanthanum fluoride treatment. Consequently, the bismuth phosphate treatment is referred to herein for background although the present invention is concerned particularly with the treatment of the fluoride'typev of carrier precipitate. That is, the present invention concerns the treatment of the fluoride type of precipitates, exemplified by lanthanum fluoride precipitates carrying Pu, or other fluoride materials such as potassium plutonium fluoride. In processes of the aforementioned type, either combination processes Where several different types of carriers are used in which a fluoride carrier precipitation is accomplished in at least one of the steps, or processes wherein fluoride compounds are more or less directly precipitated, these fluoride precipitates carrying Pu or comprising a fluoride compound of Pu may present difliculties of redissolution. For example, these fluoride compounds may resist direct dissolution in acids. Consequently, prior to my invention a procedure termed metathesis was developed which included treating with alkali hydroxides, precipitates which presented difficulties of dissolution. This has been carried out by adding potassium hydroxide to the lanthanum fluoride carrying Pu in a suitable mixing vessel in order to perform an exchange reaction and convert the lanthanum compound to the hydroxide. The lanthanum hydroxide carrying Pu may then be dissolved in acids.

While the process of the prior art is in successful, use, in some instances this standard metathesis has been found not to give as complete dissolution as desired and a residue remains in which Pu may be lost. Also in certain large scale operations materials such as grease may become incorporated in the process thereby presenting diificulties as respects dissolution of carrier precipitates.

In accordance with the present invention, there is provided an alternative method of dissolving fluoride types of compounds of or containing Pu, which process may be employed either in place of standard procedure under normal circumstances or Where other types of procedures are not satisfactory or desired under the particular circumstances involved.

That is, by the present invention utilizing some of the same steps which have been previously worked out, but supplemented and altered in certain respects the advan tage of improved reaction may be obtained as will be described.

The meaning of the terms bismuth phosphate type of process, wet fluoride type of process, product precipitate, and similar terms will be apparent as the description proceeds.

This invention has for one object, to provide improvements in methods for the separation and recovery of plutonium values.

Another object is to provide a method of separating plutonium values by a procedure characterized in that in certain steps diflerent reagents and procedure than have heretofore been used are employed.

Still another object is to provide a procedure for dis solving fluoride compounds carrying or otherwise containing Pu values.

Still another object is to provide a procedure for dissolving fluoride carrier precipitates containing Pu values of the present application.

3 which may more or less resist dissolution by usual dissolution methods.

Still further object is to provide a process for the dissolution of fluoride materials which maybe used' in place of or in conjunction with, usual dissolution processes.

Still another object is to provide certain new and imsheet, Fig. 1.

proved operations which lend themselves to the use of V and to coupling with steps already known or practiced for the separation and recovery of a Pu value.

Another object is to provide a type of process which may .employ some of the materials .used in existing processes and which may be carried out in existing equipment without change, or with a minimum of equipment change. 'Still another object is to provide a process for the recovery of Pu values which may be applied to fluoride iprecipitates containing Pu values either in relative small or large amounts. a

Still another object is to provide a method of ultimately .pbtaining anacid solution of certain fluoride materials -that resist direct-dissolution in acid.

Other objects will appear hereinafter.

For a further understanding of the invention, reference will be made to.the attached drawings forming a part In these drawings, diagrammatic representations of embodiments of the invention .aregiven in the form of flow sheets. Fig. 1 is a flow sheet for illustrating the coupling of the procedure of my invention with certain other steps. Fig. 2 is a flow sheet .showing in greater detail an embodiment of the steps pertaining particularly to my invention.

It has been found that Pu in admixture With various extraneous material may be separated and concentrated by the use of the series of steps involving the utilization of a fluoride carrier precipitate type of treatment. These treatments'are in accordance with known practice. How- -ever, I "have found that the further processing of such carrier precipitates may be rendered simpler and more efiicient by interposing the improvement features described herein such as the use of a different type of dissolution procedure and other variations. By the utilization .of these features, not only are the advantages pre- -viously obtained in the processes still obtainable, but ad- --vantages are obtained such as the dissolution of fluoride precipitate and Pu away from certain residues and the easier removal of fluoride 'ions from the resultant hydroxide precipitates.

The types of carrier precipitates involved are described in'app'lication Ser. No. 519,714, filed January 26, 1944, Thompson and Seaborg, aforementioned and reference is made to that applicationfor further disclosure, details "thereof being omitted from the present disclosure except where necessary to an understanding of the present invention; As .setfforthin said application, it has been discovered that plutonium has more than one oxidation state, "including a lower oxidation state or states herein referred to as Pu in which the element is characterized by forming insoluble phosphates and fluorides and a higher oxidation state or states referred to as Pu in which the element forms soluble phosphates and fluorides.

The aforementioned type of processes, namely the bismuth phosphate procedure and the fluoride procedure, a

are conducted under acid conditions. It has heretofore been customary to dissolve the fluoride carrier precipiof fluoride materials of the class indicated may be accomplished by using a carbonate type of solvent as dejQl'ibed in detail herein. .taeili ated un r certain dif ren s t a ons uch as in th N only is he dis olu presence of grease or upon residue resisting dissolution by standard. methods bu the m h d of dissolution may be carried out in place of the standard procedure if desired.

A general understanding of the application of my process in the field ,of separation and recovery of Pu values may be hadby reference to the attached flow In this'figure the source of materials containing iPu values is indicated at 1. This source is exemplified by a nitric acid solution of uranyl nitrate, which has resulted from or has been subjected to preliminary treatments exemplified by extraction and decontamination by the bismuth phosphate method. The solution may be oxidized at 2 and subjected to a standard fluoride byproduct precipitation step for eliminating fission products and other undesired components. The oxidized solution from 2 containing Pu is reduced at 3 in any conventional manner, and under the reduced conditions a lanthanum fluoride product precipitation applied at 4.

Referring now to the portion of the overall process to which my invention is particularlydirected, this lanthanum fluoride precipitate containing Pu values (product precipitate) after being separated in a conventional manner such as by centrifuging is then treated with-5a. potassium carbonate type solvent of the present invention at 5. It has been found that, depending upon the character of this precipitate and similar factors, a large ,portion if not all of the precipitate readily dissolves and may be withdrawn to point 6.

The carbonate solution is treated at 7 with a source of hydroxide ions for precipitating lanthanum hydroxide at '8. This lanthanum hydroxide carries the Pu and is in '15 from step 14 at this point in the process may be considered to have been exhausted of their Pu content and may be discarded.

Referring further to 5, as indicated, dependent upon the particular fluoride material treated, the bulk thereof if not all, is dissolved and may be processed through the cycle just described. However, any undissolved lanthanum fluoride precipitate such as the material *in the 1,5 of Fig. 1 may be broken down into a series of steps.

That is, in the preferred and large scale operation my inevent the original precipitate is-contaminated with grease or other additions, is conducted to treatment at 16. Further carbonate dissolution additions are applied at 17. The resultant carbonate solution may be combined with [the solution at 6, or the resultant carbonate solution may be rconducted to 18 where it is treated at 19 with KOH in a manner'cornparable to operation 7. The resultant lanthanum hydroxide may be combined with theprecipitate in operation 18.

vention respecting the use of a carbonate solvent for dissolving fluoride materials would preferably be accomplished by using several different concentrations of carhonate solutions, several different steps of making the .additions, several .different steps in carrying out washings, and transfers from the centrifuge and other similar .steps- Ihat l r fe i g 2 t first p s'o h operation under A' comprises adding at least two additions of carbonate solutions to the fluoride precipitate. As indicated on Fig. 2, this step may be carried out in a centrifuge, agitation accompanying the carbonate additions.

The residue from the primary carbonate addition as indicated at B may then be treated with further additions of a weaker carbonate solution. This residue remains in the centrifuge bowl, the dissolved portion having been conducted to the precipitation step designated C. The solutions resulting from B are conducted to C as may be the first washings from the centrifuge bowl. However, the later washings and residues from the centrifuge bowl may be discharged to Waste or recovery treatments already referred to.

In step C the addition of a source of hydroxide ion is accomplished corresponding to operation 7 of Fig. 1. This operation is carried out in a standard reaction vessel such as a precipitator with an agitator. The resultant mixture of lanthanum hydroxide precipitate and supernatant liquor is then returned to the first-mentioned centrifuge or other centrifuge where the lanthanum hydroxide precipitate carrying Pu separates out in the centrifuge bowl. This lanthanum hydroxide precipitate is subjected to a series of washes with dilute alkali hydroxide solution and water as indicated under D of Fig. 2. The final washed lanthanum hydroxide precipitate is collected at E and may then be further processed in accordance with operation in 9, 10, and 11 referred to under Fig. 1 of the flow sheet.

The process of the present invention concerns particularly the dissolution of LaF precipitate. The process may be employed in several ways, namely, to dissolve the entire LaF precipitate, or the process may be used in conjunction with the standard metathesis procedure for treating any residue remaining from standard metathesis.

A still further understanding of my invention will be had by consideration of the following examples:

EXAMPLE I A standard LaF precipitate carrying Pu was treated with a 45% solution of K CO This solution was added in the proportion of about 30 cc. of the aforementioned 45% K CO solution for each gram of lanthanum present. The reaction proceeds slowly at room temperature. Hence, it is preferred to carry out the treatment within the range of 50 C. to 95 C. for more rapid dissolution. The K solution was added to the LaF precipitate in several steps. That is, additional steps of K CO treatment were made to that portion of the LaF precipi tate which had not gone into solution by the previous K CO additions.

After the LaF precipitate had been dissolved in the K CO solution, the resultant solution was treated with KOH which precipitates La(OH) carrying Pu. The resultant La(OH) with Pu was then dissolved in nitric acid in accordance with standard procedure, and the resultant acid solution further treated in a usual manner for Pu concentration.

EXAMPLE II Several runs have been carried out for applying the process of the present invention to relatively pure samples of LaF In the first of these 250 mg. of La (as LaF containing 2.4 mg. of Pu were obtained from another concentration process. The LaF was dissolved in 17 cc. of 45 K CO which was added in two portions: 12 cc. and 5 cc. Each portion was heated for 30 minutes at 90 C. The undissolved residue after two K CO treatments contained 0.9% of the Pu; the K CO KOH waste solution obtained after precipitating the La(OH) with KOH contained 0.1% of the Pu; and the very small residue which remained after dissolving the La(OH) in HNO had no Pu. The Pu recovery in this case was 99%.

A second 250 mg. sample of La (as LaF containing 14 mg. of Pu was obtained. The LaF was dissolved'by two additions of 45% K CO using 6 cc. each time and heating for one hour at 50 C. The undissolved residue from these two K CO treatments contained 0.05% of the Pu, while the waste K CO +KOH solution contained 0.03% of the Pu. On dissolving the La(OH) with HNO there was no residue remaining. In this case the product recovery was 99.6%.

EXAMPLE III A number of runs have been made with plant type LaF precipitates. These samples had usually been through a BiPO extraction and decontamination cycle before changing the carrier and the precipitation of LaF In the first run, which was an extraction precipitate, the product in the final oxidized solution had been reduced with NaAsO then precipitated with 6.65 gm. of La. Considerable UF was present in this LaF precipitate. The LaF was treated with 300 cc. of 45% K CO at C. for 1 hour. H 0 was also added to oxidize the U+ The solution was then centrifuged and the residue treated again with cc. of 45 K CO at 90 C. for 1 hour; then centrifuged. 10 N KOH was added to each of these K 00 solutions to make them 2 N in KOH. The La(OH) precipitates were combined after washing once with 5 N KOH and twice with water. The waste K CO +KOH solutions were separately analyzed. The La(OH) precipitate was dissolved in HNO leaving a small residue. The material undissolved after two K CO treatments was treated with 6 N HNO giving a yellow solution and a black residue. The final results of this run are summarized below. No analysis was made of the starting material.

Percent Pu (1) Final La (N09 product solution 93 (2) 1st K CO +KOH waste solution 3.3 (3) 2nd K CO +KOH waste solution 0.5

(4) 6 N HNO solution of K CO insoluble res- In this example 93% of the Pu was found in the product solution. Aside from the 3.3% diversion of Pu which was I-INO soluble and which could be recovered, the only other substantial diversion of Pu was that of 3.3% in the waste K CO -i-KOH solution.

In the second run with plant LaF the final oxidized solution was reduced with Pe and H 0 before precipitating with 6.65 gms. of La. In this run the solution of LaF with K CO was carried out at 50 C. The LaF was treated with 330 cc. of 45% K CO for 1 hour at 50 C. After centrifuging, the residue was treated with cc. of 45% K CO for 30 minutes at 50 C. The residue remaining was washed twice with 20% K CO solution. The washings and the two K CO solutions were combined. La(OH) was precipitated by making the solution 2 N in KOH. The La(OH) was washed once with 5 N KOH and twice with H O; then dissolved with HNO giving a clear solution plus a small residue. This solution is referred to below as 50 C. La(NO product solution.

The undissolved residue after the two K CO treatments at 50 C. was heated with 50 cc. of 45% K CO for 1 hour at 99 C. to determine whether any La still remained. La(OH) was precipitated as before (an amount of that previously precipitated was found). This La(OH) was dissolved in HNO giving a clear solution and a small residue. This solution is referred to below as 90 C. La(NO product solution.

treatment at 90 C.

No analysis of Percent Pu (1) 50 C. La(NO product solution 91.0

(2) Residue remaining after dissolving 50 C.

La(OH) -in HNO 0.4

.(3) 50 C. K CO +KOH waste solution 3.5

(4) 90 La(NO product solution r 3.2

(5) Residue remaining after dissolving 90 C.

' La(OH 0.1

-(6) 90 K CO +KOH waste solution (7-) 6 N HNO solution of K CO insoluble residue 1.5 (8) Residue insoluble in K CO and HNO 0.05

p The results of this run indicated that while two treatments with 45% of K CO at 50 C. gave substantial recovery, in some instances a third step may be applied since an additional 3% of the Pu was recovered by the In this run, however, during the K CO extractions a bulky Fe(OH') precipitate was present (Fe+ had been used as the reducing agent). The 'waste K CO +KOH supernatant contained 3.5% of the Pu. However, the total recovery of Pu was 94% and further recovery may be accomplished by ancillary steps.

As illustrated above a number of runs have been performed on the conversion of LaF to La(NO by means of the 'K CO procedure. Some of the runs were conducted with relatively pure LaF prepared in the laboratory, and others with LaF- obtained from plant operations. The LaF wasusually treated with two portions of K CO after treatment with the first portion, the residue was treated with a smaller portion. The .undissolved residue was washed once or twice with a K CO solution, and the'cornbined K CO solutionsand washes made ,2 N in KOH to precipitate La(C)H)3. After wash ingonce with KOH and twice with H O, the La(OH) was dissolved in HNO A small residue may remain after dissolving the hydroxide in I-INO In general the diversions of Pu were 1% or less when the procedure was applied to laboratory LaF but higher diversions were obtained with more impure LaF from the plant. The highest diversion of Pu appeared to occur in the residue' remaining after K CO treatment and in the K CO KOI-I supernatant. In those cases in which an appreciable amount of Puremains in the K CO residue,

:it appears that a further K CO extraction of the residue EXAMPLE IV In order to recover Pu remaining in the K CO 'KOH waste solution when plant 'LaF was treated, the following work was conducted. A standard KOH metathesis was performed on the plant LaF but aninsoluble residue remained which contained about 85% of the Pu. A small aliquot of this residue was treated twice with 45% K CO at 95 C., and La(OH) precipitated by making the K CO solution 2 N in KOH. About 99% of the product was found in the HNO solution of La(OH) and 0.4%

in the tablet 8 Table.-Recove ry o;f Pu from K CO KOH Supernatant by addition of La La" added mg./cc. in each Number of Total La Percent Pu addition Additions mg. lcc. Carried The above procedure is essentially carrying of Pu by a preformed La(OH) precipitate, and better recovery was obtained when the 'La+ was added in several separate additions. The results indicate that about 95% of the Pu which may remain in the K CO KOH waste solution may be recovered by addition of two 0.1 mg./cc. portions of La.

EXAMPLE V In view of the fact that work indicated that two K CO treatments would in general be adequate for dissolving LaF check runs were conducted to determine whether two treatments at C. for /2 hour each would usually be satisfactory.

'A portion of plant LaF containing large amounts of Bi was washed twice with 2 N I-ICI to remove Bi therefrom. This reduced the amount of solid material by about onehalf. The solid material remaining was treated with K CO in a manner similar to that already described. About 81.2% of the Pu was found in the first K CO solution, 17.0% in the second K 00 solution; and 2% in the K CO washes; the Pu was therefore quantitatively extracted in this run. The K CO -insoluble residue contained only 0.4% of the product. Despite the HCl wash used in this example, considerable Bi was still present, but the K CO extraction was successful despite its presence. These results indicate that two K CO treatment at 60 C. for /2 hour each are generally adequate to give good Pu recovery.

EXAMPLE VI 7 by treatment with concentrated HCl, but a maximum of only 68% was removed. Another small aliquot of the residue was treated with 2 portions of 45% K CO 'at 7 95 C., and La(OI-I) precipitated bymaking the com- 70 in the K CO KOH waste solution. La+ was added to a V the latter solution in several different ways in order to recover the product remaining in it. Conditions for the La+ addition andthe results obtained are'summarized bined K CO solutions 2 N in KOH. The HNO solution of the La(OH) contained 99.6% of the Pu.

' EXAMPLE VII In accordance with this example batches of LaF .of

' plant type were routinely processed by the K CO method with satisfactory results, in instances where KOH metathesis appeared inadequate. No trouble was encountered in the K CO method'due to grease or oil. It appears that the first plant batches had picked up a certain amount of grease. The largest diversion of Pu encountered in the procedure was the '12% Pu remaining in the K CO KOH supernatants. The amount of Pufound in other waste fractions. was very small. Two 45% K CO 9 making the solution 2 N in KOH and adding La+ to precipitate La(OH) carrying Pu.

The diversion of Pu in K CO --KOH supernatant is probably a simple solubility effect since in some runs where the amount of plutonium has been greater the percentage diversion in this waste solution has only been of the order of 0.3%.

EXAMPLE VIII In accordance with this example, the materials treated were similar to the plant materials described under Example V. However, in this particular instance, the ma terials contained a substantial amount of iron presumably dissolved from the stainless steel equipment used in carrying out prior treatment of the materials. The LaF precipitate containing iron was treated in standard manner as above described with several potassium carbonate additions. However, in the first carbonate addition there Was included a content of ammonium sulfide in an amount to provide a concentration of approximately 0.05 M.1 M thereof. A precipitate of iron sulfide formed which separated without loss of Pu thereby reducing the content of iron to a noninterfering amount. The Pu and other components dissolved in the carbonate solution in a manner the same as in the preceding examples. The treatment with potassium hydroxide and other regular processing was carried out.

By elimination of the iron the Pu subsequently isolated is more suitable for forming the peroxide derivative and for other similar purposes where a content of iron might promote decomposition.

EXAMPLE IX In accordance with this example other materials containing a content of iron in the amount of 23x10 M was treated. The materials otherwise contained usual amounts of lanthanum and other components.

Treatments with 45% potassium carbonate were applied and wash treatments with 20% potassium carbonate as already described were also applied. However, the first carbonate addition contained about 0.05 M ammonium sulfide. The iron content was reduced to about 1.2x 10" M namely by a factor of about 20.

From the foregoing therefore it is apparent that the K CO -solution metathesis has proved to be a very satisfactory method for treatment of fluoride type precipitates. The K CO method of the present invention is particu larly useful in situations involving difiiculties due to the presence of grease and other impurities.

The process may be applied to materials containing small amounts of Pu, such as tracer amounts or to materials containing relatively large amounts such as present in plant materials. The exact amount of Pu present is not a limitation on my invention. The quantities and concentration of reagents used are not a limitation upon the invention but are set forth herein as a guide to preferred operation. In general, in processes of the type described, in order to obtain favorable volume reductions and concentration, it is usually desirable to keep the quantities to a minimum consistent with good operation. However, this does not preclude the use of excess amounts of reagent if this should be desired.

Although the preferred solvent reagent comprises ptassium carbonate, the reagent may be modified. For

, example, cesium and rubidium carbonates may be used.

That is, it is believed that it is a concentrated source of carbonate ions that can be heated which provides the desired solution action. Hence, certain modifications of the solvent which do not alter this action may be made. The alkali hydroxides or similar aklali reagents may be employed in conjunction with the carbonate. The term carbonate solvent used herein is intended to embrace such a variety of solvents. While the use of potassium hydroxide has been described in the examples as the preferred reagent for supplying the source of hydroxyl ions to obtain a lanthanum hydroxide precipitate, other sources of hydroxyl ions may be utilized. Sodium hydroxide is exemplary of such other reagents. In place of the use of lanthanum ion added for the recovery of Pu from the waste hydroxy-carbonate solution, other additions which cause the formation of an insoluble hydroxide may be used. For example, primary mention may be made of utilizing a source of bismuth ions in place of the lanthanum ions. Other metallic ions which may be used are exemplified by thorium, uranium, zirconium, and strontium.

As indicated, the process may be carried out in standard equipment. The fluoride materials containing Pu to be dissolved may be collected in a conventional solid bowl centrifuge and there treated with the carbonate solvent. The solution resulting may be centrifuged out and conducted to other conventional equipment for further treatment. It will be observed that in many instances at least dissolution is accomplished in the first treatment with the carbonate solvent. By the application of the other auxiliary steps described, substantially complete recovery may be obtained.

Although the process has been described in connection with the treatment of a fluoride material carrying or containing Pu, exemplified by lanthanum fluoride treated in a centrifuge, as this represents conditions frequently encountered in plant operations, my invention is not limited in these respects. For example, other materials such as plutonium fluoride, potassium plutonium fluoride, potassium lanthanum fluoride and the like may be treated by my invention. Likewise, rather than carrying out the dissolution in a centrifuge, the process may be carried out in tanks in a manner analogous to tank metathesis used industrially. Or other apparatus may be used.

According to the best evidence available, the oxidation state of plutonium secured in solution by the action of the oxidizing agents referred to herein and in cited co-pending application Serial No. 519,714, now US. Patent No. 2,785,951, is greater than four, the oxidation state secured in solution by the action of the reducing agents referred to herein and therein is no greater than four. It should therefore be understood that, as used herein, Pu and Pu in the (0) condition (or state)" are both synonymous with plutonium in an oxidation state greater than four and Po and Pu in the (r) condition (or state) are both synonymous with plutonium in an oxidation state no greater than four.

I claim:

1. In processes for plutonium recovery which comprise carrier precipitation of plutonium values from solution with a lanthanum fluoride carrier precipitate, and subsequent derivation from the resulting plutonium-bearing carrier precipitate of an aqueous acidic plutonium-containing solution, the improvement method in said derivation which comprises contacting said carrier precipitate with a concentrated aqueous solution of potassium carbonate to effect dissolution therein of at least a part of said precipitate, including said plutonium values, separating the resulting solution from any remaining precipitate and contacting said remaining precipitate with an aqueous solution containing at least '20 percent by weight of potassium carbonate to effect dissolution therein of said remaining precipitate, and thereupon combining the resulting solutions and incorporating therein an alkali metal hydroxide to a concentration of at least approximately 2 normal to precipitate lanthanum ions consequently contained therein, as lanthanum hydroxide, and concomitantly carrier precipitate therewith said plutonium values therefrom.

2. In processes for plutonium recovery which comprise carrier precipitation of plutonium values from solution with a lanthanum fluoride carrier precipitate, and subsequent derivation from the resulting plutonium-bearing carrier precipitate of an aqueous acidic plutoniumcontaining solution, the improvement method in said derll ivation which comprises vcontacting said carrier precipitate with an aqueous potassium carbonate solution of substantially 45% by weight concentration to cited dissolution therein of at least a part of said precipitate, including said plutonium values, separating the resulting solution from anyremaining precipitate and contacting said remaining precipitate with an aqueous potassium carbonate solution of substantially 20% by Weight concen- .tration -to effect dissolution therein of said remaining precipitate, and thereupon combining the resulting solutions and incorporating therein potassium hydroxide to a concentration of approximately 2 normal to precipitate lanthanum ions consequently contained therein, as

lanthanum hydroxide, and concomitantly carrier preipi tate therewith said plutonium values from said combined resulting solutions.

References Cited in the file of this patent pages 608, 669 (1924). Longmans, Green & Co., London; a 

1. IN PROCESSES FOR PLUTONIUM RECOVERY WHICH COMPRISE CARRIER PRECIPITATION OF PLUTONIUM VALUES FROM SOLUTION WITH A LANTHANUM FLUORIDE CARRIER PRECIPITATE, AND SUBSEQUENT DERIVATION FROM THE RESULTING PLUTONIUM-BEARING CARCRIER PRECIPITATE OF AN AQUEOUS ACIDIC PLUTONIUM-CONTAINING SOLUTION, THE IMPROVEMENT METHOD IN SAID DERIVATION WHICH COMPRIESE CONTACTING SAID CARRIER PRECIPITATE WITH A CONCENTRATED AQUEOUS SOLUTION OF POTASSIUM CARBONATE TO EFFECT DISSOLUTION THEREIN OF AT LEAST A PART OF SAID PRECIPITATE, INCLUDING SAID PLUTONIUM VALUES, SEPARATING THE RESULTING SOLUTION FROM ANY REMAINING PRECIPITATE AND CONTACTING SAID REMAINING PRECIPITATE WITH AN AQUEOUS SOLUTION CONTAINING AT LEAST 20 PERCENT BY WEIGHT OF POTASSIUM CARBONATE TO EFFECT DISSOLUTION THEREIN OF SAID REMAINING PRECIPITATE, AND THEREUPON COMBINING THE RESULTING SOLUTIONS AN INCORPORATING THREIN AN ALKALI METAL HYDROXIDE OT A CONCENTRATIONOF AT LEAST APPROXIMATELY 2 NORMAL TO PRECIPITATE LANTHANUM IONS CONSEQUENTYL CONTAINED THEREIN, AS LANTHANUM HYDROXIDE, AND CONCOMITANTLY CARRIER PRECIPITATE THEREWITH SAID PLUTONIUM VALUES THEREFROM. 